The present invention relates to fluid-dispensing nozzles generally, and to micro-scale ink-jet nozzles used in high resolution color and gray scale printing in particular.
Ink-jet printers have rapidly gained in popularity as a means for generating a high quality color and gray scale images from computer sources. Because of the large drop size produced by most ink-jet printers, the color and gray scale images they produce are limited to less than 10 color tone or gray scale levels per atomic picture element (pixel). Although this is adequate for certain applications such as business graphics and color highlighting, it is unquestionably inadequate for making accurate representations of real world colors and does not approach a true photographic appearance.
An ink-jet device makes color images by physically mixing ink on the print medium to obtain a desired color. Inks for a color ink-jet printer are generally selected from one or more of black, magenta, cyan, and yellow colors. The inks generally contain less than 25% colorant and other additives in a water-base vehicle for jetting. Presently known devices include those operating at a resolution of 300 pixels per inch (ppi), wherein each of the jetted drops are sized to fill a 0.08xc3x970.08 mm2 pixel for printing on standard imaging papers and media, and also those operating at a resolution of 150 ppi, wherein each of the jetted drops are sized to fill a 0.17xc3x970.17 mm2 pixel for printing on highly ink-absorbing medias such as cotton textiles or unsized papers or for printing large images to be viewed from distances of more than about 5 feet such as signage. Because of the above-described large size drops, the said devices are limited in the gradation of color saturation and shade, and thus in the realism that they can provide as a result of this limitation. However if the individual ink drops can be made smaller, the number of ink drops deposited per pixel can be increased, and it is possible to vary the number of ink drops deposited within a pixel to obtain a wide gradation of color saturations and shades, enabling photographic quality coloring.
It is known that a range of zero to thirty droplets per 0.08xc3x970.08 mm2 pixel per color printed on standard image media or per 0.17xc3x970.17 mm2 pixel per color for signage or highly ink-absorbing media enables the creation of hundreds of different color saturations and shades discernible by the human eye. Thus, it would be desirable to provide a group of nozzles capable of providing thirty or more droplets per pixel.
In addition to the appropriate control software and inks, the above described color and gray scale image production using ink-jet technology requires ink-jet nozzles capable of consistently dispensing the very small droplets of ink. Any imperfections in the ink-jet nozzle orifice can cause a dispersion or deflection of the ink-jet with disastrous consequences for the print quality, especially when the jetting pattern of four or more nozzles must be coordinated.
In order to obtain photographic quality color and gray scale images using an ink-jet device, a nozzle with an orifice approximately 15 microns or less in diameter is required for standard imaging media, or 30 microns or less for signage or highly ink-absorbing media such as cotton textiles or unsized papers. Whatever the selected diameter of the nozzle for a given ink-jet printer product, it is necessary that the manufactured nozzle diameters vary by no more than xc2x10.6 microns so that the printed color saturations and shades do not vary perceptibly from printer to printer. It is known in the art to fabricate ink-jet nozzles from glass tubes, but because of the difficulty in manufacturing a nozzle having such a small orifice size from a glass tube, it is desirable to provide a method of consistently providing nozzles of the precise dimensions needed.
One prior art ink nozzle is illustrated in U.S. Pat. No. 22 3,393,988 to Blumenthal, wherein a nozzle having an orifice 0.003 to 0.0004 inches is formed by heating the lower end of a vertically oriented, low melting point, glass tube with a flame burner until it melts into a tear-drop shape under the influence of gravity, thereby forming a converging inner passage that is abruptly tapered (60 to 90xc2x0 average included angle with respect to the central axis of the passage). Glass at the end of the tube is then removed to establish an abruptly converging passageway with a central orifice which is subsequently flame polished to provide smooth surfaces.
It should be noted that Blumenthal""s requirement that the tube be oriented vertically, due to the technique""s reliance on the force of gravity, is a severe manufacturing limitation. It should also be noted that Blumenthal specifically teaches away from a gently tapered converging portion leading to the orifice. Were such an abruptly tapered end as shown in Blumenthal be ground in an attempt to provide an orifice five times smaller, with the precision, perfection and symmetry required for photographic quality color or gray scale printing, the results would be uncertain. Furthermore, even if a 30 micron or less diameter orifice were to be obtained, the flame polishing step of Blumenthal would exacerbate grinding-induced flaws in the orifice edge and produce an unacceptable variation in the diameter of the orifice with respect to the requirements for the above described printing applications. Even further, such an abrupt taper leading to the orifice results in an additional burden on the grinding process in that a more stringent criteria for orifice perfection and symmetry is necessary to assure a steady and well-directed ink-jet stream.
The drawing or pulling method of making a converging passage, specifically rejected by Blumenthal, is described in U.S. Pat. Nos. 3,986,636 and 4,111,677. As Blumenthal indicates, drawing a glass tube causes a reduction in passage diameter gradually over such an extended distance that it causes fluid flow problems. In order to draw a glass tube, a relatively large portion of the tube must be made molten, and glass in its molten state is very hard to dimension with accuracy.
Additionally, pulling a heated glass tube to cause narrowing of a central passage causes a concomitant reduction in wall thickness. The resulting drawn portion of the glass tube is therefore extremely fragile even at the diameters taught by Blumenthal, and is extraordinarily so in a tube one tenth the size. Reinforcement of the fragile drawn tube is demonstrated in a fluid-dispensing device, the 9103557E173E manufactured by Siemens-Elema AB of Sweden, which provides a metal sheath over the tube, except in the area of the orifice where the tube is uncovered.
Therefore, in addition to the other above-recited features lacking in the prior art, it would be desirable to provide a nozzle having an inner wall leading to an orifice with a less extensive taper than a drawn tube, yet more taper than the Blumenthal nozzle, and capable of being manufactured with a precision orifice in the thirty micron or less range. It would further be desirable to form such a nozzle without weakening it so that it is unmanageably fragile or so that it requires reinforcement. It would further be desirable to provide a nozzle which can be formed in any position from the vertical to the horizontal.
In surmounting the foregoing disadvantages, the present invention provides a fluid-dispensing nozzle having an inner passage that tapers to an orifice approximately thirty microns or less in diameter, making possible the creation of photographic-quality color and gray scale images using an ink-jet printer. The nozzle provides a perfectly symmetrical fluid dispensing inner passage having a gentle taper formed without pulling or drawing the glass tube, and can be fabricated in any orientation from the horizontal to the vertical. The inner passage provides a taper having an angular change with respect to the axis of symmetry of the nozzle sufficient to minimize fluid flow problems encountered in drawn tubes without being an abrupt taper, while the outer diameter of the nozzle in the area of the orifice is at least as large as along the remainder of the nozzle""s length. The nozzle is fabricated so that exceptional accuracy is possible during an orifice dimensioning step of fabrication. Furthermore, the nozzle is sufficiently robust to withstand handling an incidental contact without breaking.
In accordance with the invention, a nozzle for an ink-jet printer is provided having a gradually converging inner diameter leading to an orifice less than 15 microns in diameter for standard imaging media or less than 30 microns in diameter for highly ink absorbing media, and having an outer nozzle diameter proximate the orifice at least as great as the outer diameter at other points along the nozzle.
The nozzle is produced by heating a tube while rotating it, until a portion of the tube is sufficiently softened to cause the inner diameter to converge at an angle between 5 and 25 degrees with respect to the axis of symmetry of the tube, and until the inner diameter is less than a selected orifice diameter. A length of tube is then removed having an inner diameter less than or equal to the selected orifice diameter resulting in an orifice at an end of said heated tube.
The ink-jet nozzle of the invention is central to a printing process, wherein a printhead having a plurality of nozzles supplied with ink is responsive to a computer system capable of generating color raster image data. In accordance with the color raster image data, the printhead deposits ink droplets from one or more of the nozzles in the pixels required to form a two-dimensional image. The nozzles are supplied with black ink for gray scale images and differently colored inks for color images. Such a fluid-dispensing nozzle can be used advantageously for biological and medical devices and apparatuses, such as cell sorting flow cytometers and reaction creating and controlling instruments, and pharmaceutical devices and apparatuses, such as drug or pill manufacturing instruments.